1. Field of the Invention
The present invention relates generally to an electronic closed loop air-fuel ratio control system for use with an internal combustion engine, and particularly to an improvement in such a system for properly initiating the operation of the system in consideration of exhaust gas temperature.
2. Description of the Prior Art
Various systems have been proposed to supply an optimal air-fuel mixture to an internal combustion engine in accordance with the mode of engine operation. One such system is to utilize the concept of an electronic closed loop control system based on a sensed concentration of a component in exhaust gases of the engine.
According to the conventional system, an exhaust gas sensor, such as an oxygen analyzer, is deposited in an exhaust pipe for sensing a component of exhaust gases from an internal combustion engine, and for generating an electrical signal respresentative of the sensed component. A differential signal generator is connected to the sensor for generating an electrical signal representative of a differential between the signal from the sensor and a reference signal. The reference signal is previously determined in due consideration of, for example, an optimum ratio of an air-fuel mixture to the engine for maximizing the efficiency of both the engine and an exhaust gas refining means. A so-called proportional-integral (p-i) controller is connected to the differential signal generator, receiving the signal therefrom, and generating a signal therefrom. A pulse generator is connected to the p-i controller for receiving the signal therefrom and for generating a train of pulses based on the signal received. These pulses are fed to an air-fuel ratio regulating means, such as electromagnetic valves, for supplying an air-fuel mixture with an optimum air-fuel ratio to the engine.
In the previously described conventional control system, however, a problem is encountered as follows. The output voltage of the exhaust gas sensor is considerably low when the exhaust gas temperature is low during idling or during continuing low engine speed operation. Therefore, according to the prior art, the operation of the air-fuel ratio control system is inhibited until the output voltage of the exhaust gas sensor rises up to a predetermined level. However, if, for example, an oxygen analyzer is used as the exhaust gas sensor and the air-fuel mixture fed to the engine is lean, then the output voltage of the exhaust gas sensor is low in spite of the fact that the exhaust gas temperature is sufficiently high. Therefore, the operation of the conventional air-fuel ratio control system can not be properly initiated in that it is not exactly determined whether or not the actual low output voltage of the exhaust gas sensor results from the low temperature of the exhaust gas. Proposals to obviate the above described defect of the prior art, have not proven practical or satisfactory.